The invention relates to electric lamps and, more specifically, to electrodeless fluorescent lamps operated at low and intermediate pressures at frequencies from 20 KHz to 1 MHz.
Electrodeless fluorescent lamps have been recently introduced in markets for indoor, outdoor, industrial, and commercial applications. The advantage of electrodeless lamps is the removal of internal electrodes and heating filaments that are a life-limiting factor of conventional fluorescent lamps. Therefore, the life of electrodeless fluorescent lamps is substantially higher than that of conventional fluorescent lamps and can reach 100,000 hrs.
An electrodeless fluorescent lamp introduced in the market by General Electric Corp. (under the trademark GENURA) is operated at a frequency of 2.65 MHz and used for indoor general lighting. This lamp is a replacement for the R30 incandescent lamp and has 1,100 lumen light output at 23 W of total power. The life of GENURA lamps, 15,000 hours, is much larger than that of incandescent lamps. The drawback of GENURA lamps is the high initial cost, partially due to the need to prevent electromagnetic interference and partially due to the circuit cost in operating at 2.65 MHz. Both drawbacks could be diminished if the electrodeless fluorescent lamp was operated at lower frequencies, as low as 100 KHz.
In U.S. Pat. No. 6,081,070 by Popov et al. and in U.S. patent application Ser. No.09/303,951 by Chamberlain et al. (having the same assignee as the present application) electrodeless fluorescent lamps operated at low frequencies from 50 KHz to 500 KHz were described. Those lamps utilized a ferrite core made from MnZn material, Litz wire, and an aluminum cooling structure that removed heat from the reentry cavity walls and the ferrite core and redirected that heat to the lamp fixture. The aluminum cooling structure comprises an aluminum cylinder insider the ferrite core and an aluminum base welded to the lamp fixture. This approach and construction were found to be very effective to keep the ferrite core at temperatures below its material Curie point.
However, in many lamp applications (e.g. the replacement of a conventional incandescent lamp) the large and heavy metal (aluminum or copper) base is not suitable due to its large size and weight. Also, the replacement. of the incandescent lamp requires the use of Edison socket that should be coupled with the base. Again, the diameter of the lamp base should not be larger than the diameter of the incandescent lamp bulb that is 60 mm.
The proximity of ferrite core to the metal base causes the interference of the magnetic field with the metal base that results in the increase of the coil/ferrite core power losses. Indeed, the magnetic field generated by the coil induces eddy currents in the metal base that causes power losses and reduces the combined coil/structure quality factor, Q. As a result, the lamp power efficiency and hence, efficacy decreases.
The need for the incorporation of the lamp driver and lamp matching network inside the lamp base and to couple them with the Edison socket makes the cooling issue more complex. Indeed, the temperature inside of the lamp base should not exceed xcx9c100xc2x0 C. to provide integrity of the driver""s components. The use of components that can stand higher temperatures leads to higher cost of the driver and hence, the lamp.
The present invention comprises an electrode-less fluorescent lamp that includes a glass envelope containing a fill of inert gas with mercury vapor. A ferrite core and an induction coil made from Litz wire are positioned inside of the reentrant cavity. A cooling structure comprises a metal (aluminum, copper) tube placed inside of the cavity and a ceramic spacer that is glued to the Edison socket with material having high thermal conductivity.
An objective of the present invention is to provide a cooling structure that keeps the ferrite core temperature below Curie point.
Another objective of the present invention is to provide low temperatures, T less than 100xc2x0 C., inside of the lamp base where the driver and matching network are placed.
A further objective of the present invention is to provide low power losses in the cooling structure and in the lamp base so to provide a high lamp power efficiency and efficacy.
Yet another objective of the present invention is to design a coil that has high quality factor at the frequency as low as 100 KHz so as to provide low coil power losses and high lamp power efficiency.
An additional objective of the present invention is to provide an electrodeless fluorescent lamp that can operate at 100 KHz that results in overall low cost system.